DESCRIPTION (from applicant's abstract) The wiring pattern of the adult nervous system is dependent upon a series of sequential axon guidance events that occur during neuro- development. Neuronal growth cones respond to a variety of guidance cues that are both attractive and repulsive and that act over short and long distances. Little is known, however, about the signal transduction events that mediate these guidance decisions. An essential first step in obtaining an understanding of the molecular mechanisms that underlie these events is identification of the receptors that bind these cues. The central focus of this proposal is an analysis of the molecular basis of repulsive growth cone guidance during neurodevelopment. Uncovering the molecular mechanisms that translate an extracellular repulsive cue into an alteration in the growth cone cytoskeleton is likely to be of clinical significance in the development of therapeutic strategies directed toward promoting nerve regeneration following injury or degeneration, and also towards understanding the basis of certain developmental disorders. The applicant has shown that the axonal glycoprotein neuropilin-1 is a functional receptor for the long-range repulsive guidance cue semaphorin III (Sema III). Further, his lab has demonstrated that neuropilin-1 is but one member of a family of related proteins through the identification of neuropilin-2. The semaphorins are a large family of proteins containing several members that have been shown to function in repulsive guidance. Sema III is one of the very few repulsive cues for which a receptor has been identified and for which in vivo repulsion assays are well established. To elucidate the molecular basis of semaphorin-mediated repulsive guidance the applicant will examine the roles neuropilins play in this process. His group will determine the precise neuronal expression patterns of neuropilins 1 and 2 during development. The spatial and temporal distribution of neuropilin ligands during development and the range of different semaphorins capable of binding to each neuropilin will also be determined. Functional characterization of both neuropilins will include assessment of neuropilin function in primary rat neuronal culture systems and in vivo genetic studies in mice. Finally, the semaphorin-neuropilin receptor complex will be defined biochemically, with respect to both extracellular and intracellular components required for semaphorin- mediated repulsive guidance.